Molecular alterations characteristic of glioblastoma include the amplification of EGFR and the loss of the PTEN tumor suppressor, which lead to the constitutive activation of the PI3K/Akt pathway and provides the rationale for our focus in this Project on a unique PI3K inhibitor, PX-866 (ProIX). This wortmannin analog offers three key improvements: 1) it is biologically stable; 2) it is a more potent inhibitor of the p110-a subunit of PI3K and 3) it is a weaker inhibitor of p110-p, and so shows much reduced dose limiting ontarget toxicity common to all PI3K inhibitors. We plan to test the hypothesis that the PI3K inhibitor PX- 866 is an effective therapy for glioma by evaluating it in preclinical models and in the clinic in early phase clinical trials for glioblastoma. However, the limited success of signal transduction inhibitors used as single agents, which is most likely due to compensatory or collateral pathways, is a strong rationale for exploring combination therapies. Some combinations can be suggested on the basis of current knowledge of signaling pathways, and we propose to test the most compelling in our models and the clinic. At the same time we plan to identify additional molecular target(s) or pathway(s) that would, once they are blocked by another drug, confer synergy to a PI3K inhibitor, based on siRNA synthetic lethality screening. Together these efforts will test the hypothesis that combination therapies based on PI3K inhibitors are effective in the treatment of glioma. Our Specific Aims are 1) To study PX-866 and rational combinations in improved preclinical culture and animal models of glioma, using xenografts of human glioma cells that retain the molecular hallmarks of the parental tumors and on brain cancer stem cells. Rational combinations include PX-866 and the small molecule drugs Tarceva, Sorafenib and rapamycin/RADOOl as well as the standard of care - radiation and temozolomide; 2) To initiate clinical trials of PX-866 and rational combinations, based on the data obtained in Aim 1; and 3) To identify novel synergistic targets for rational drug combinations with PX-866 using siRNA synthetic lethality screening. By completing these Aims we will pursue, in parallel, the clinical deployment of a promising PI3K inhibitor and the development of combination therapies based on it. Both rational (Aim 1) and newly discovered (Aim 3) co-targets/therapies will be developed, allowing both near-term and mid-term combination therapies to follow the individual lead compound (Aim 2) into clinical evaluation. Therefore this project emphasizes the translational dimension of our signal transduction research program with the hope of accelerating promising new treatment to the bedside.